Yarn package in the form of a rod-shaped batt



NOV. 26, 1968 w DAVlS ET AL 3,413,185

YARN PACKAGE IN THE FORM OF A ROD-SHAPED BATT Filed Sept. 30, 1964 |5FIG. 2 )0 H INVENTORS THOMAS WADE DAVIS ROBERT JOHN GILARDI ATTORNEYUnited States Patent 3,413,185 YARN PACKAGE IN THE FORM OF A ROD-SHAPEDBATT Thomas Wade Davis, Petersburg, and Robert John Gilardi, Richmond,Va., assignors to E. I. du Pont de Ncmours and Company, Wilmington,Del., a corporation of Delaware Filed Sept. 30, 1964, Ser. No. 400,353 7Claims. (Cl. 161-169) ABSTRACT OF THE DISCLOSURE A back-windable yarnpackage in the form of a rodshaped batt of longitudinally collapsed,continuous, plexifilarnentary strand material. Process for forming thepackage by flash-spinning a polymer solution to produce a plexifilament,then causing the plexifilament to enter axially of an elongatedpasasgeway and to impinge at a right angle upon a yieldable surface.Apparatus for carrying out the process including a spinneret, atubularshaped perforated conduit extending out from the spinneret todefine an elongated passageway, and means for restraining the forwardmovement of the batt in the passageway.

Specification This invention is concerned with a back-windable batt ofcontinuous strand material.

Introduction In the commercial production of textile yarns variousmethods are known for collecting yarns at speeds above 3000meters/minute in a flat package, cake, or batt which is adapted to beeasily unwound provided certain prescribed patterns have been observedin collecting the strand. This type of package typically containshelically deposited coils or loops in contrast to straight-woundpackages such as those Wound on cones or bobbins. Straight-woundpackages are not satisfactory for collecting strands at very high speedbecause traverse difi'iculties and analogous problems are created by themotion of the collecting device. Strands which have heretofore beencollected in the form of a flat package, cake or batt have generallyconsisted of multifilament yarns in which the single filaments areseparated from one another, the filaments being generally larger than 8microns in thickness.

In U.S. Patent 3,081,519 of Blades and White a fibrillated type ofstrand is described which consists of a three-dimensional integralplexus of synthetic organic, crystalline, polymeric fibrous elements,the fibrous elements being in the form of film-fibrils less than 4microns thick. The film-fibrils within these strands have greatattraction for one another, presumably because of electrostatics orbecause of their planar structure and high surface area. Consequently ithas been found particularly diflicult to obtain a package from whichsuch a strand can be removed continuously without entanglement.

Accordingly the purpose of the present invention is to provide aback-windable package of a fibrillated strand wherein the strand iscomprised of an integral network of film-fibrils. It is an object toprovide such a package which is in a form suitable for shipping,particularly in a form which can be pulled off continuously as a fluffytow and converted into cigarette filters or other items where bulk isdesired.

Summary of the invention The above objectives are accomplished byproviding a rod-shaped batt of longitudinally-collapsed, continuous icestrand material, the strand material comprising a threedimensionalintegral network of film-fibrils of crystalline oriented syntheticpolymer, the film-fibrils having an electron difiraction angle of lessthan and an average film thickness of less than 4 microns. The batt hasrecoverable strand ends at each of its opposite ends and has a densityof about 1 to 15 lbs./ft. The collapsed network is composed of tinyfolded film-fibrils or filmfibril composites. The total packagecross-sectional area is advantageously between one and four times thatof the network. The strand material in the batt lacks any sort ofwinding pattern or twisted or piddled configuration; i.e. the strandmaterial has simply collapsed upon itself somewhat like the action thatoccurs in the bellows of.

an accordion.

The apparatus of the invention comprises, in combination, a spinnerethaving an orifice for producing a strand of filamentary material andcollecting means for receiving the filamentary material upon itsissuance from the spinneret. The collecting means comprises atubularshaped conduit extending out from the orifice to define anelongated passageway therein, a first end of the passagewaycommunicating with the orifice whereby filamentary material isdischarged under elevated pressure from the orifice into the conduit. Asecond end of the passageway is remote from the orifice. Means isprovided in the passageway for restraining the forward motion of thebatt. For example, the cross-sectional area of the passageway maydiminish, i.e. narrow or gradually taper, from the first end to thesecond end. This enables the freshly-spun filamentary material toaccumulate by collecting upon itself. Also the conduit includes meansfor maintaining the pressure within the passageway at a level betweenthe spinning pressure and atmospheric pressure. In a preferredembodiment the means for maintaining the pressure within the passagewaywill comprise simply a series of spaced apart perforations in theconduit in the vicinity of the first passageway end. In any case, thepressure in the passageway, which will be somewhat above atmospheric,causes the collected batt to slowly extrude from the downstream openingof the passageway. The rod-shaped package so produced will thus haveessentially the same cross-sectional configuration as the opening.

The rod-shaped batt of longitudinally-collapsed fibrillated strandmaterial is made by spinning a solution of organic polymer through thespinneret orifice, the solution upstream of the orifice being underpressure at a temperature above the boiling point of the solvent. Thesolution passes through the orifice into an enclosed enlongatedpassageway or collecting zone which is at substantially lower pressurebut which is nevertheless at greater than atmospheric pressure. Afibrillated continuous strand comprising a three-dimensional network isformed at the orifice exit. The strand expands and impinges atessentially a right angle against a yieldable collecting surface zone.In this way it is caused to collapse longitudinally, eg in the directionof spinning. The lateral or cross-sectional dimensions of theaccumulated batt are governed by the size and shape of the walls whichdefine the passageway. These walls may comprise a generally cylindricalor tubular shaped conduit. The cross-sectional area of the passagewaymay be equal to or greater than the maximum cross-sectional area of thestrand network but, in either case, should be small enough to preventfolding of the gross strand in zig-zag arrangement. The gaseous solventwhich separates from the polymer at the orifice is allowed to expand inthe collecting passageway partially by pushing the collecting surfaceand filamentary material away from the orifice and partially by escapethrough holes in the walls defin- 3 ing the passageway. The collapsedfibrillated network piles up continuously and is forced continuouslyfrom the collecting passageway by means of gas pressure created thereinso as to extrude a continuous rod-shaped batt into the surroundingatmosphere.

The invention will be further described with reference to the drawingswherein:

FIGURE 1 is a drawing of a rod-shaped batt of strand material comprisinga longitudinally-collapsed integral three-dimensional film-fibrilnetwork.

FIGURE 2 is a drawing in perspective, partially in cross-section, of aspinneret and strand collector and showing extrusion of a rod-shapedbatt.

FIGURE 3 shows a spinneret and collecting chamber, partially incross-section, the tubular conduit being generally rectangular incross-section, the top wall being hinged at its upstream end.

FIGURE 4 is a drawing, partially in cross-section, of a spinneret andstrand collector, in this case the tubular conduit is a perforatedcylinder provided with an obstruction in the nature of an end closure.

FIGURE 5 is a drawing of a spinneret suitable for use in the apparatusof FIGURES 2, 3, or 4.

Back-windable batt The product of this invention, herein referred to asa batt, is similar in some respects to the cocoon spun by the silkwormin that the strand may be removed continuously and is composed of verytiny fibrous elements. In other ways the batt difiers greatly from acocoon. For example, the batt is made in the form of a long rod or stickand the strand can be removed from the end of the package, actuallyeither end, without rolling the rod or developing torque in the strand.

Considering FIGURE 1 in more detail the product comprises a longrod-shaped batt 1 with recoverable ends 2 from a single strand. Thestrand is composed of a three-dimensional integral network offilm-fibril elements 3. The film-fibril elements are connected at randomintervals along and across the strand and are less than four micronsthick.

The strand is a plexifilament as described in US. Patent 3,081,519 toBlades et al. It is prepared from synthetic filament-forming polymers orpolymer mixtures which are capable of having appreciable crystallinityand a high rate of crystallization. A preferred class of polymers is thecrystalline, non-polar group consisting mainly of crystallinepolyhydrocarbons, e.g. polyethylene, polypropylene, and copolymers ofethylene and propylene. Common textile additives such as dyes, pigments,antioxidants, delusterants, antistatic agents, reinforcing particles,adhesion promoters, removable particles, ion exchange materials, and UV.stabilizers may be mixed with the polymer solution prior to extrusion toprovide strands containing such.

Referring again to FIGURE 1, because of the nature of the strandcollector the batt is usually concave on one end 4 and convex on theother end 5, the convex end being thefirst spun end. It is usuallyeasier to remove the strand continuously from the concave end, butremoval is actually possible from both ends. An interesting feature ofthis strand package is the ease with which it may be divided intosmaller packages. By simply bending the rod vigorously it can be dividedinto two parts, each with two recoverable strand ends. These ends remainintact during the package breaking operations, but may be cut like theumbilical cord after separation of the two package parts. Although therod-shaped package is extruded continuously from the apparatus and canbe made in interminable length, it is conveniently broken intoapproximately 6 foot lengths for packaging in side-by-side relationshipin boxes for shipping. It is also possible, however, to ship thematerial in continuous form by coiling as is done with telephone cableor electric wiring.

The density of the tow package may be regulated by means to be describedfurther hereinafter in connection with the process details. The densityof the product should be, however, between about 1 and 15 lbs./ft.

The strand which can be removed from either end of the package comes offin the form of an integral network. The network normally takes the formof a cone during removal; the apex being pointed in the direction ofstrand travel during such removal. The periphery of the network at thebase of the cone is generally circular, but within the circularperiphery are multitudinous film-fibril elements which are beingsimultaneously withdrawn in random fashion from all parts Within thecircular area. The base of the cone may oscillate somewhat within theboundaries of the package during removal but there is preferably noappreciable zig-zag folding of the entire strand in the package. If thestrand is initially removed with little or no compaction it is in afluffy, high bulk, three-dimensional form, frequently with a density aslittle as a few hundredths of a pound per cubic ft. In this form it isessentially indistinguishable from a bulky plexifilamentary strand whichhas been simply spun into the atmosphere without the aid of a collectingdevice.

To preserve the plexifilamentary multifibrous network character, thecross-sectional area of the package should not be more than about fourtimes the cross-sectional area of the base of the cone, i.e., less thanfour times the cross-sectional area of the integral film-fibrilnetworkat any point in the package. In the preferred product, thecross-sectional area of the package is less than 1.5 times that of thefilm-fibril network. This means that in remov ing the strand from an endof the package, at any given time film-fibrils are being lifted fromessentially all parts of a generally circular area, the size of thatarea being at least one-fourth, but preferably at least two-thirds, thecross-sectional area of the package. Whereas the lateral dimensions ofthe strand network and package may be nearly equal, the latter will havea length of the order of th to th that of the strand before packing.

A desirable feature of the package is the ease with which it may beconverted to a flufiy high bulk tow. The simple process of pulling thestrand from the package causes it to bloom, i.e. to form a soft bulkytow which is satisfactory for textile uses and for preparing cigarettefilters. Many other uses, including amusement devices, will also beapparent for the package because because of its unique ability to giveseemingly infinite lengths of a bulky strand from a small size package.The easy blooming of the tow is understandable if one considers themethod of film-fibril deposit in the package. Essentially the networkhas never been compacted transversely; it has simply been collapsedlongitudinally to remove the bulk of the air that normally fills thespaces between filmfibrils in the network. The film-fibrils are foldedindividually or as composites, but in general the total strand does notfold.

Although the specific description is limited here to rodshaped packagesof circular and rectangular cross-section, it will be evident that avariety of cross-sectional configurations may be formed to suit theintended use. In general, shapes such as rectangular which can be boxedwith a minimum loss in space are preferred.

Considering now the plexifilamentary strand itself, the strand is formedby extruding a solution of a fiber-forming polymer in a liquid which isa non-solvent for the polymer below its normal boiling point, at atemperature above the normal boiling point of the liquid, and at autogenous pressure or greater into the atmosphere or other medium of lowertemperature and substantially lower pressure. The vaporizing liquidwithin the extrudate forms bubbles, breaks through confining walls, andcools the extrudate, causing solid polymer to form therefrom. Theresulting multi-fibrous yarn-like strand has an internal fine structureor morphology which may be characterized as a three-dimensional integralnetwork or plexus consisting of a multitude of essentiallylongitudinally extended interconnecting random length fibrous elements,hereafter referred to as film-fibrils, which have the form of thinribbons of a thickness less than 4 microns. The film-fibril elements,often found as aggregates, intermittently unite and separate atirregular intervals called tie points in various paces throughout thewidth, length and thickness of the strand to form an integralthree-dimensional plexus. The film-fibrils are often rolled or foldedabout the principal film-fibril axis, giving the appearance of a fibrousmaterial when examined without magnification. The strand comprising athree-dimensional network of filmfibril elements is referred to as aplexifilament. The plexifilaments are unitary or integral in nature,meaning the strands are one piece of polymer, are continuous in nature,and the elements which constitute the strand are cohesivelyinterconnected. Minor physical treatments of the continuous strand suchas shaking, washing, or textile processing will not cause appreciableamounts of the filmlike elements to separate from the strand.

For the purpose of simplifying the visualization of the fibrillatedplexifilament strands, one may suppose that all the morphologicalelements of the plexifilament are derived from bubbles in the viscoussolution which form rapidly as the pressure is reduced during theinitial stage of conversion of fiuid polymer to strand material. Thebubbles then grow and rupture in various ways to form the multifibrousnetwork. The extreme thinness of the pellicular material impartsdesirable aesthetic properties such as softness and suppleness toplexifilaments and enables them to be easily discernible frommulti-fibrous strands or coarsely porous fibers of the prior art.

The strands are continuous in nature and can be produced in essentiallyendless lengths. The whole strands can have deniers as low as or as highas 100,000 or even higher. The highly fibrillated strand has theappearance of sliver or tow from extremely fine fibers. The filmfibrils,however, are connected in a network, there being few it any unconnectedfibril ends.

The strands of this invention generally have tenacities of at least 1.0g.p.d. and, when drawn, may have tenacities as high as 23.0 g.p.d. Thestrands are twisted 8 t.p.i. prior to making the measurement.

All of the strands are characterized morphologically by athree-dimensional network of film-fibril elements. These networks mayexist in various forms, but in all cases the film-fibrils are extremelythin. On the average the filmfibril thickness is less than 4 micronsthick. In the preferred products the film-fibrils are less than twomicrons thick and may indeed have a thickness of less than 1 micron. Thefilm-fibril elements are normally at least five times as wide as theyare thick, the actual width being between about 1 micron and about 1000microns.

The film-fibril elements in plexifilaments are found in the form offibril composites which are laminates, aggregates or bundles within thegross strand. Because these fibril composites continuously divide andparts of them join other bundles, it is difiicult to count individualfilmfibrils in the strand. However, for convenience, the average numberof fibril composites in a 0.1 mm. thick crosssectional cut of the strandis used as a meaure of the degree of fibrillation. The number of thesefibril composites per 1,000 denier in a 0.1 mm. length of strand ishereafter referred to as the free fibril count. It is recognized thatthe number of additional film-fibrils which can be pulled away from thefibril composites with slight tension will be many times the numberfound already free, but film-fibrils which adhere to each other are notcounted as separate fibrils in the standard test.

The predominantly longitudinal orientation of the filmfibrils of allplexifilamentary strands is readily apparent from the fact that all suchstrands are much more resistant to tearing or breaking transversely thanto splitting length-wise. The general coextensive alignment of thefibrous elements in the direction parallel to the strand axis is easilydiscernible to the naked eye for most plexifilamentary species.

The plexifilamentary strands of the invention are made of crystallinepolymerlt has been found that the pellicular material in the as-spunstrand when consisting of a crystalline polymer is substantiallyoriented as measured by electron ditfraction, i.e., it has electrondiffraction orientation angles smaller than 99. It is believed that thehigh strength of the plexifilamentary strand as spun is closely relatedto the crystalline orientation within the film-like ribbon and in thestructural arrangement of the fibrils themselves in the strand. In thepreferred crystalline oriented products of the invention, thefilm-fibrils have electron diffraction angles of less than 55 Theorientation of the crystallites in the film-fibrils is in the generaldirection of the film-fibril axis.

X-ray diffraction patterns which are obtained using the whole strandinstead of just film-fibrils show a substantial amount of orientation inthe strand as spun. The X-ray diffraction orientation angles are lessthan 55 in the preferred embodiments of the invention. The substan tialorientation which is exhibited by the gross strands indicate that notonly are crystallites oriented along the fibrils, but the fibrils arethemselves oriented in the general direction of the strand.

The plexifilament strands have a surface area greater than 2 m. /g., asmeasured by nitrogen adsorption methods. Due to the extremely highpolymer/air interfacial area the strands have marked light scatteringability and high covering power.

An important characteristic of the strands of this invention is thefibrillar texture of the gross strand as' observed with the polarizingmicroscope.

In order to observe fibrillar texture, a specimen is prepared asfollows: a short length of strand is frozen in liquid nitrogen and asegment which is 1-5 millimeters long is cut from the frozen strand. Thesegment is placed on its side in immersion oil on a microscopic slide,and the slide its side in immersion oil on a microscopic slide, and theslide is placed in a vacuum chamber and pumped down to remove trappedair. After removing the slide from the vacuum chamber, the specimen isobserved in a polarizing microscope using about 45X magnification. Afirst order red plate is used in the microscope and the Nicols prismsare crossed at to one another.

A striking color view of the sample is seen in the polarizingmicroscope. In the strands of this invention long streaks of uniformcolor run parallel to the strand axis. Although there are a variety ofcolors, each color extends for long periods along the length of thestrand. An interpretation of the polarized light patterns may be foundin Fiber Microscopy, by A. N. J. Heyn, Interscience Publishers, 1954,pp. 288352. Monochromatic streaks in color photomicrographs taken withpolarized light are derived from areas of equal optical path differenceand in general will be due to equal orientation and equal thickness inthe strand. These photographs demonstrate therefore that the strandshave a high degree of organization, and the highly organized areasextend for considerable distances along the length of the strand. Thestrands are characterized as fibrillar if at least half of the materialmaking up the strand appears as monochromtic streaks when observed inthe polarizing microscope. The monochromatic streaks are oriented in thedirection of the strand axis and have an actual (unmagnified) length ofat least 0.2 mm. The monochromatic areas are considered as streaks whenthey have a length at least 10 times the width.

Characterization methods for the plexifilamentary strand are furtherdescribed in U.S. 3,081,519 referred to above. These methods and otherdescriptive matter of the patent are incorporated herein by reference.

The melt index of the polymer is the flow in g./ 10 min., as determinedby ASTM Method D1238-57T, Condition E, and is inversely related tomolecular weight. By linear Spinneret and strand collector The apparatusof the invention will be described by reference to FIGURE 2, whichrepresents one embodiment. As shown therein, the spinneret 6 is providedwith an orifice 7 through which a solution 8 of a synthetic organicpolymer is extruded by means of high pressure derived from the solventvapor by pressure at temperatures above the boiling point, or thepressure may be exerted by combinations of solvent vapor pressure withmechanical pressure, pressure of inert gases, or other pressurizingmeans.

Surrounding the spinneret orifice 7 and extending axially from it is atubular shaped conduit 10 defining an elongated collecting passageway 9.As will be seen the conduit 10 is in the nature of an elongated conicalelement of generally circular cross-section, the diameter andcross-sectional area gradually diminishing toward the downstream endthereof. Conduit 10 is open at the down.- stream end 11 to emit the battproduct 1. The wall of the conduit 10 is perforated with numerous holes12, particularly in the vicinity of the upstream end thereof. Inoperation the solution is forced through the orifice 7 into thecollecting passageway 9, whereupon the solvent evaporates suddenly,forming a three-dimensional network 13, which collects on the surface 14of the previously formed batt 1. Part of the expanding gas escapesthrough holes 12. The remaining gas, which will usually be at a pressureof .1 to 100 p.s.i.g, acts to compact the previously formed batt andforces the collected material continuously out the opening 11 Theconduit 10 has an interior diameter at its upstream end approximatingthe outside diameter of the spinneret. It can thus be fixedly mountedupon the spinneret and secured to it by any convenient means such as aclamp, not shown.

The process is self-controlling when sufficient hole area is provided inthe collecting passageway for release of the maximum amount of solventvapor generated. Thus when pressure in passageway 9 is not sufficient tomove the batt, the impacting yarn builds up and covers holes, therebyreducing the open area for vapor escape. Pressure increases by thismechanism until it is sufficient to move the batt. When pressure in thepassageway exceeds equilibrium, the collected batt of filamentarymaterial accelerates and uncovers more holes, thereby increasing theopen area for vapor escape. Pressure thereby decreases until equilibriumis obtained. Although the collected batt may move intermittently, itwill generally proceed at a constant rate of speed once pressureequilibrium has been achieved.

The pressure in the passageway may, of course, be reg ulated further bypressure control valves in a gas escape port or bleed-off line incommunication with the passageway. Alternatively the frictionalcharacteristics of the collecting tube, e.g. in terms of taper or otherobstructions, can also be varied to affect the pressure and thus therate of extrusion and batt density. In any case the pressure in thepassageway should be kept at a level sufiicient to cause the rod-likebatt to extrude continuously from the passageway at a rate between 1/25and 1/3000th of the strand formation rate. The operator will have nodifficulty in adjusting one or more variables so as to cause theextrusion process to proceed smoothly and efliciently at a desired rate.

It is apparent that a vapor collector can be installed surrounding theperforated chamber for recovery of solvent.

The package density can be varied by adjusting the size of the outletend of the collecting conduit and the degree to which thecross-sectional area of the conduit decreases as that end is approached.By varying one or both of these factors, the amount of pressure neededin passageway 9 to move the batt will be altered. The shape and size ofthe package can be varied widely depending upon the geometry anddimensions of the conduit and opening.

One function of the collecting device is the provision of a pressurizedchamber between the spinneret and the collected batt with means forbleeding OK or venting excess vapor at a rate consistent with the rateat which solution is spun through the orifice. The system developssuflicient pressure in operation to eject the batt completely out of thetubular conduit if holes or other means for venting the tube are notused. A further function of the collecting device is to enable controlof the forward travel of the batt. In this respect the tubular conduit10 of FIGURE 2 uses friction developed by the batt in contact with theinner peripheral wall of the tapered tube to balance the force developedby vapor pressure; however, other devices which also restrain forwardmotion will be apparent.

The spinneret orifice diameter must be small enough to permit continuousreplenishment of the solution supply upstream of the spinneret atconstant pressure and must be large enough to maintain a constant andmoderate pressure (e.g., .1 to p.s.i.g.) in the collecting passagewayunder the conditions of temperature, pressure and solution concentrationused for the particular solution being spun. To accomplish thisobjective the total area of the holes in the collecting zone must bekept at a level which is consistent with the spinneret orifice size.

In designing the apparatus, the various dimensions should be selected tocause the expanded flash-spun strand to impact the surface of thealready collected batt at a point where the network has first reachedits maximum diameter. If the surface of the already collected batt istoo close to the spinneret, the velocity at impact causes tearing of theweb which results in yarn breaks during backwinding. In addition thestrand tends to fold and arrange itself transversely with respect to theaxis of the package. If the point of formation is too far from thespinneret, the yarn will tend to be deposited parallel to the axis ofthe package or will be blown completely out of the collector. Theparallel type of yarn arrangement cannot be backwound without excessiveyarn breakage.

When the dimensions of the collecting conduit and the gas escape portshave been appropriately selected for the polymer flow rate, spinneret,and solution concentration being used, batt formation will occur at thepoint where the yarn reaches its maximum diameter. In this case, theyarn will be longitudinally collapsed without excessive gross foldingand can be readily backwound by pulling on the free end.

Under a given set of operating conditions to permit impact of the strandat a point farther away from the spinneret, the taper of the collectingtube may be reduced, giving thereby less resistance to the collectedcake. Alternatively the size of the opening 11 in the collecting tubemay be decreased giving higher pressure in the tube. This also causesthe rod-like package to extrude at higher speed.

Another embodiment of the apparatus of the invention is shown in FIGURE3, shown partially in cross-section. Here means are provided to enableadjustment of the taper of the collecting passage during the collectingoperation. The spinneret 6 is enclosed by a collecting conduit, showngenerally as 21, which is rectangular in cross-section. The spinneretorifice passage 7 is oriented horizontally as is the collecting conduit.The upper or top wall 22 of the horizontally mounted conduit fitsclosely between the adjacent side walls 23 and 24 but is notstationarily attached. It is pivotally mounted at its upstream end by ahinge 15, the hinged top wall 22 being in close-fitting relationshipwith the two adjacent side walls 23 and 24. The hinged top 22 and theopposite side 25 are perforated throughout their lengths. The other twosides 23 and 24 are not perforated. The hinged side is forced againstthe batt by means of weights 26. In operation the collecting conduit hasthe shape of a truncated wedge. The unperforated sides 23 and 24 of thecollecting chamher are sufficiently large to provide for sealing thechamber regardless of the positions of the hinged side 22. A rodlikebatt with rectangular cross-section is obtained from this apparatus.

The embodiment of the apparatus shown in FIGURE 4 is made of aperforated round tubular element 31, nearly a right circular cylinder.It is attached to the spinneret by means of hose clamp 37. Near thedownstream end thereof is a closure plate 32 pivotally mounted andsecured by hinge 33. The plate 32 is adapted to engage and rest upon thebatt 1 as it extrudes from the opening 11. A weight 34 is afi'ixed toarm 35 which extends from plate 32. The weight assists in creating thefriction needed to control the speed of the extrusion and hence thepressure in the passageway. An extension 36 of tubular element 31prevents the Weight of closure plate 32 and associated parts frombreaking the batt 1. In starting up the process, the downstream end 11is closed by plate 32. It remains closed until sufiicient filamentarymaterial accumulates, whereupon the batt begins to extrude and lift theplate 32 to the position shown.

FIGURE is a drawing of a suitable spinneret for use in the apparatus ofthe invention. As shown the spinneret may be provided with a prefiashingor pressure let-down zone to facilitate a high rate of bubblenucleation. Solution enters the spinneret through constriction 42 andpasses to the let-down chamber 43 and finally is extruded throughspinning orifice 7 into the surrounding atmosphere. This spinneret, ofcourse, must be designed for a specific throughput rate. As described inaforementioned U.S. Patent 3,081,519, wide variations can be made in thespinneret design.

Process elements Full details of the flash-spinning process aredescribed in aforementioned US. Patent 3,081,519. In addition, however,there are further process features which are related to obtaining arod-like package within a specified density range, having goodback-windability and being free of knots, slubs, bubbles, or otherdefects in the continuous network structures.

With respect to previously known process elements, solvents for use informing the high temperature, high pressure polymer solutions requiredfor forming the plexifilaments of the invention should preferably havethe following characteristics: (a) a boiling point at least 25 below themelting point of the polymer used; (b) they should be substantiallyunreactive with the polymer during extrusion; (0) they should dissolveless than 1% of the high polymeric material at or below its normalboiling point; and (d) the solvent should form a solution which willundergo rapid phase separation (i.e., in less than .01 second) uponextrusion forming a non-gel polymer phase, i.e., a polymer phasecontaining insufiicient residual solvent to plasticize the structure. Inthese requirements, the flash spinning process employed in the presentinvention differs radically from conventional solution spinningtechniques since in the latter the spinning solvent is invariably asolvent for the polymer below the normal boiling point, usually even atroom temperature.

Among those liquids which may be advantageously utilized in theflash-spinning process (the actual choice of course depending upon theparticular polymer used) are aromatic hydrocarbons such as benzene,toluene; aliphatic hydrocarbons such as butane, pentane, hexane,heptane, octane, and their isomers and homologs; alicyclic hydrocarbonssuch as cyclohexane; unsaturated hydrocarbons; halogenated hydrocarbonssuch as methylene chloride, carbon tetrachloride, chloroform, ethylchloride, methyl chloride; alcohols; esters, ethers; ketones; nitriles;amides; fiuorocarbons; sulfur dioxide; carbon disulfide; nitromethane;water; and mixtures of the above liquids.

The flashing off of solvent during the spinning process of thisinvention is similar in some respects to the fiash evaporation ofsolvent in flash distillation procedures. The rapid and substantialreduction in pressure upon the confined polymer solution when theorifice is reached results in the production of bubbles within the stillfluid polymer followed by expansion of the bubbles and evaporativecooling of the polymer to form pellicular material which ruptures anddeforms with resultant production of the characteristic integral plexus.The initial heat content of the spinning solution will affect the finalmorphology. If the initial heat content is too small, a closed cellmorphology will result and if too high, a sintered product will beproduced. It is surprising that despite the violent nature of theprocess, indefinitely continuous strands may be obtained.

The preferred fibrillated species which is suitable for use in theback-windable package, is composed of linear polyethylene. It isadvantageously flash-spun from spinning solutions of 10 to 14% by weightpolymer in trichlorofiuoromethane. The temperature upstream of thespinneret should be above the critical temperature minus 45 C. for thesolvent, but preferably is even higher, being preferably above thecritical temperature minus 30 C. In addition, for purpose of the presentinvention the pressure of the solution upstream of the spinneret shouldbe far above the normal vapor pressure of the solvent at the temperaturementioned, the additional pressure being exerted by mechanical means,such as by a reciprocating pump. The pressure should be kept above thetwo-liquidphase pressure boundary, this being the pressure for a givensolution below which two liquid phases can exist. For example, a 14%solution of linear polyethylene of melt index 0.57 intrichlorofluoromethane which is spun at C. requires a pressure of atleast about 1285 p.s.i.g. to exist as a homogeneous single-phasesolution upstream of the spinneret. The vapor pressure of the solvent at185 C. is 515 p.s.i.g. The additional pressure to obtain 1285 p.s.i.g.must be supplied mechanically. The two-liquid-phase pressure boundarymoves to higher pressure with increasing temperature, with increasingmelt index (decreasing polymer molecular weight), or with decreasingsolution concentration. US. Application Ser. No. 308,845 now Patent No.3,227,794 of Anderson and Romano filed Sept. 13, 1963, provides afurther explanation of this phenomenon and hence the disclosure thereofis incorporated herein by reference.

A further requirement for consistently obtaining a highly fibrillateduniform product is that the solution pressure should be dropped to apressure which is below the two-liquid phase pressure boundary, justbefore passing through the final spinneret orifice. For a 14% solutionof linear polyethylene in trichlorofiuoromethane this let-down pressureshould be between 700 and about 1100 p.s.i.a.

In polymer-solvent systems where two liquid phases form readily, thedrop in pressure in the let-down zone causes two liquid phases to form,with tiny droplets of one phase being carried in the second phase. Thetiny droplets apparently act as bubble nuclei and promote an extremelyhigh degree of fibrillation in the threadline when it emerges into thesurrounding air at atmospheric pressure. Maximum fibrillation is ofparticular importance for achieving the greatest degree of opacity, bulkand other desirable (fiber properties. Arrangement of the pressures inthe system so that the pressure in the flow line upstream of theconstriction is above the twophase pressure limit, assures theattainment of such high degrees of fibrillation. As an added safeguardfor a commercial installation employing typical available high pressureequipment, a pressure drop from at least 25 p.s.i. above the two-liquidphase pressure to at least 25 p.s.i. below that pressure is desirablyprovided.

A spinneret which is suitable for providing the necessary pressurelet-down is shown in FIGURE 5 described above. It is, of course, quitesatisfactory to use other pressure let-down systems such as are providedby automatic valves and pressures controlling mechanisms.

The solution which flashes from the final spinneret orifice passes tothe collecting passageway which is maintained at pressures substantiallybelow that of the pressure let-down chamber. In order to providecompressive force for the collected strand material this pressure shouldbe above .1 p.s.i.g. On the other hand it should be kept below about 100p.s.i.g. to promote rapid evaporation of solvent and to avoid completeexpulsion of the collected batt from the conduit. Preferably thepressure is between 0.1 and 5.0 p.s.i.g. The pressure in the collectingchamber is measured by means of a conventional pressure gauge.

The solvent which is used in the flash-spinning process must be capableof rapidly separating from the polymer when cooled. As explained inforegoing paragraphs it is also necessary to add sufficient heat to thesolution upstream of the spinneret to provide all of the calories neededfor vaporization of the solvent upon flash extrusion so that additionalheat is not needed in the collecting chamber. A solvent which isparticularly satisfactory for this purpose with linear polyethylene istrichlorofiuoromethane.

As the plexifilamentary strand forms at the spinneret it expands into anetwork of increasing diameter and then increases no more. Optimumoperation of the process occurs when the collecting surface is placed atthe point where the strand first reaches its full diameter. When placedcloser than this the strand tends to deposit in zig-zag form or coils.When placed further away the strand loses velocity and again deposits inunsatisfactory form being laid in either longitudinal or transversezig-zag pattern.

When the collecting surface is presented an optimum distance from thespinneret, the network collapses longitudinally. The optimum distancebetween spinneret and collecting surface is generally between 0.3 and2.0 inches.

The plexifilamentary strand which is formed at the spinneret may beprovided within a broad range of deniers, by adjusting solutiontemperature, pressure, concentration, and orifice dimensions. Deniersgreater than 170 are satisfactory for most purposes. Frequently it isadvantageous for these, e.g. upon removal from the rodshaped batt, to beplied to obtain cigarette filter tows of 15,000 denier. Alternatively aheavy tow may be spun directly from a large spinneret orifice.

The following examples illustrate specific embodiments of the invention.All parts and percentages are by weight unless otherwise indicated.

Example 1 A solution of linear polyethylene in trichlorofluoromethanewas prepared continuously by pumping approximately 204 kg./hr. ofsolvent and 33.1 kg./hr. of molten polymer at a fixed ratio into a screwmixer as described in the Anderson and Romano U.S. application S.N.308,845. The polymer which was used had a melt index of 0.5 and adensity of 0.95 g./cm. A 14% solution was delivered continuously to anautomatic pressure letdown valve at a temperature of 185 C. and apressure of 1800 p.s.i.g. The solution passed through an automatic valveto a pressure let-down chamber of 17.2 cm. capacity maintained at apressure of 775 p.s.i.g. The final orifice in the spinneret was roundand had a diameter of .117 mm. The length of the orifice passage throughthe spinneret plate was .127 mm. The spinneret face was fiat, therebeing no flare on the outside edge of the orifice and no countersink onthe inside. The spinneret orifice passage was oriented horizontally.

A plexifilamentary strand with denier 660 as backwound or 795 at 50 g.tension was spun from the orifice at the rate of 33.1 kg./hr. The strandwas spun directly into a strand collector of the type shown in FIGURE 4.

The collector was round in cross-section with inside diameter of 4.45cm. It was 33 cm. in length. The collector was attached snugly to thespinneret by means of hose clamp 37. The upstream end was perforatedalong the first 13.96 cm. with 0.16 cm. diameter holes. The holes werearranged in a square pattern, the centers being .238 cm. apart. Theseholes were polished to avoid snagging. The remainder of the collectorwas not perforated.

After the spinning operation reached equilibrium, the collectingoperation was started by closing the hinged plate at the downstream endof the strand collector. The force of a ten-pound weight urged the plateagainst the collector end. As the batt was formed the plate was pushedup to a horizontal position and the batt continuously extrudedthereunder. The gas pressure in the passageway was on the order of 1-2p.s.i.g.

The batt so formed was round in cross-section, 4.84 cm. diameter.Sections were cut from the extruded rod as it formed. These sectionswere about 1.22 meters long. The rods had a density of 7.24 lbs./ft.(.116 g./crn. The consolidation ratio was 200021, i.e., each meter ofthe rod-like batt contained approximately 2000 meters of strand. Thestrand was 660 denier. The strand ends during removal from the rod-likebatts formed a conical network with a diameter of about 4.7 cm. at thebase of the cone.

The strand ends in the rods of fibrous batt were easily recovered and asoft bulky tow could be unwound from each end, the tow being essentiallyfree of knots or slubs. Twenty-three of these rods were mounted inparallel on a creel to permit strand removal, the concave ends of eachbeing aimed in the same direction. The twenty-three strand ends werepulled off sumultaneously from the concave ends of the rods and gatheredtogether to form a tow with a denier of 15,400.

Samples of the tow, about 2.3 cm. in diameter, were passed between apair of 7.5 cm. (in diameter) rolls with a nip load of 4.4 kg./ cm. oftow width. A coherent uniform tape of 15,400 denier was prepared whichcould be rolled up on a reel similar to movie film. This tape wassubsequently used to prepare cigarette filters after rebulking bypassage through an air jet.

Example 2 A plexifilarnentary strand with denier 350 was spun by atechnique similar to that of Example 1. The strand discharged from theorifice at the rate of 20.4 kg./hr. The strand was spun directly intothe strand collector shown in FIGURE 2. The collector was round incross-section, 3.2 cm. diameter at its upstream end and approximately2.5 cm. at its downstream end. It was 27.3 cm. in length. The collectorwas attached snugly to the spinneret. The collector was perforated with0.16 cm. diameter holes along the entire length. The holes werestaggered, the centers being 0.47 cm. apart. These holes were polishedto avoid snagging.

After the spinning operation reached equilibrium, the collectingoperation was started by blocking the open end of the collector. Anequilibrium was reached between the friction of the rod against thesides of the collector and the equilibrium gas pressure in thecollector.

A continuous rod of fiibrous batt was extruded from the collector. Thebatt was round in cross-section (2.5 cm. in diameter). The rods had adensity of about 10 lbs./ft. (0.16 g./cm. The consolidation ratio wasapproximately 2000:1, i.e., each meter of the rod-like batt containedapproximately 2000 meters of strand. The strand was 350 denier.

The collector tube was provided with a longitudinal seam to enable thediameter to be reduced by an externally applied force. This diameter wasadjusted so that batt formation occurred at approximately 2.5 cm. fromthe spinneret. The strand network as it impinged on the surface of thebatt had a diameter of about 2.5 cm.

The strand ends in the rods of fibrous batt were easily recovered and asoft bulky tow could be unwound from each end, the tow being essentiallyfree of knots or slubs. Forty of these rods were mounted in parallel ona creel to permit strand removal, the concave ends of each being aimedin the same direction. The forty strand ends were pulled offsumultaneously from the concave ends of the rods and gathered togetherto form a tow with a denier of 14,100.

Example 3 A plexifilamentary strand with denier 410 was spun in a mannersimilar to Example 1, being discharged from the orifice at the rate of24.1 kg./hr. The strand was spun directly into the strand collectorshown in FIGURE 3, having a hinged top. The collector was square incrosssection, the dimensions at its upstream end being 3.5 cm. by 3.5cm. It was 31.8 cm. long. The collector was attached snugly to thespinneret. The hinged top wall and bottom wall of the collector wereeach perforated along the first 15.0 cm. There were 140 holes, each 0.16cm. in diameter. The holes in the bottom and top walls were polished toavoid snagging. The two side walls of the collector were not perforated.

After the spinning operation reached equilibrium, the collectingoperation was started by clossing the hinged side of the strandcollector. After the collector was filled with strand material afive-pound weight was attached to the downstream end of the gate.

A continuous rod of fibrous batt was extruded from the collector. Thebatt Was rectangular in cross-section (2.5 cm. x 3.5 cm.).

The application of the five-pound weight to the gate caused the surfaceof the collected batt to be formed constantly at approximately 2.5 cm.from the spinneret.

The strand ends in the rods of fibrous batt were easily recovered and asoft bulky tow could be unwound from each end, the tow being essentiallyfree of knots or slubs.

What is claimed is:

1. A yarn package in the form of a rod-shaped butt oflongitudinally-collapsed continuous strand material, the strand materialcomprising a three-dimensional integral network of film-fibrils ofcrystalline oriented synthetic polymer, the film-fibrils having anelectron diliraction angle of less than and an average film thickness ofless than 4 microns, the film-fibrils being folded along transverselines to provide an accordion-like extensibility to the strand, strandmaterial being recoverable at each of the opposite ends of said batt,said batt having a density of about 1 to 15 lbs./ft. the cross-sectionalarea of the batt being 1 to 4 times that of the collapsed strandmaterial therein.

2. A yarn package according to claim 1 wherein one end of the batt isconcave and the other is convex.

3. A yarn package according to claim 1 wherein the batt can be brokeninto rod-like portions, each rod-like portion having recoverable strandends.

4. A yarn package according to claim 1 wherein the length of recoverablestrand is between 25 and 3000 times the length of the batt.

5. A yarn package according to claim 1 wherein the strand material formsa conical configuration when tension is applied longitudinally betweenthe batt and the strand material.

6. A yarn package according to claim 1 wherein the cross-sectional areaof the batt is 1 to 1.5 times that of the collapsed strand materialtherein.

7. A yarn package according to claim 1 wherein the polymer is a linearpolyethylene.

References Cited UNITED STATES PATENTS 3,081,519 3/1963 Blades et al.3,148,101 9/1964 Allman et al. 2,372,695 4/ 1945 Taylor. 2,780,8382/1957 Wilkie. 2,947,242 8/ 1960 Guenther et al. 3,081,519 3/1963 Bladeset al.

ROBERT F. BURNETT, Primary Examiner.

L. M. CARLIN, Assistant Examiner.

